This invention is related to decapsulating packaged integrated circuits and, more particularly, those packaged integrated circuits made using copper-technology and encapsulated by a mold compound.
Integrated circuits are often encapsulated in a mold compound. After such encapsulation, it can be difficult to perform subsequent failure analysis of the integrated circuit because it has been encapsulated. One of the techniques, which is mechanical, used to expose the integrated circuits is to grind the encapsulant back until the integrated circuit has been exposed. The encapsulant can also be cut along the sides. A disadvantage of the mechanical approach is the difficulty in knowing when to stop the grinding. Another disadvantage is that any wires will be ground away.
Chemical processes that can remove the mold compound arc generally preferred. The typical chemicals used for this are nitric acid and sulfuric acid. Nitric acid has been quite successfully used for integrated circuits using aluminum technology but not with those using the more recent copper-technology. The nitric acid not only removes the mold compound but also the upper copper layer. If this happens, the top interconnect layer is not available for failure analysis. An example of an important test is the wire pull and ball shear test. This is a test of the wire-to-pad bond that is at the upper layer. Sulfuric acid also causes the same problem.
Thus, there is a need for a technique for chemically removing encapsulant of a packaged copper-technology integrated circuit without damaging the copper.